The present invention generally relates to heat and energy recovery ventilators. More particularly, the present invention relates to heat and energy recovery ventilators used to obtain thermally efficient ventilation of structures such as rooms, houses, buildings, and/or dwellings, and in particular, to those ventilators that include variable speed motors that are used to control a number of characteristics of air, heat, and humidity transfer through an enclosed space.
Heat recovery ventilators are installed in residential, commercial, and industrial buildings to extract and remove heat from one air stream and transfer the heat to a second air stream, wherein energy recover ventilators are installed in these structures to extract and remove both heat and moisture from one air stream and transfer the heat and moisture to a second air stream. In particular, rotary wheel heat and/or energy recovery ventilators are known, wherein a wheel rotates in a housing through countervailing streams of exhaust and fresh air, in the winter extracting heat and/or moisture from the exhaust stream and transferring it to the fresh air stream. In the summer, rotary wheel heat exchangers extract heat and moisture from the fresh air stream and transfer it to the exhaust stream, preserving building air conditioning while providing desired ventilation.
Blowers (e.g., a fan and a motor driving the fan) typically are used to create pressures necessary for the countervailing streams of exhaust and fresh air to pass through the heat exchanger (e.g., a rotary wheel heat exchanger). Some ventilators, however, are designed for use in existing heating, ventilating, and air conditioning (HVAC) systems that have sufficient air pressure to drive the countervailing streams, and may or may not also include blowers.
Such ventilators are generally fabricated using a metal internal support structure to provide a mechanical support function, i.e., connect and support all the internal components such as motors, fans, heat exchanger, etc. Typically, these ventilators also include an insulation layer outside of the internal support structure to prevent condensation from building up in and on the ventilator. Finally, an outer housing of sheet metal is placed over the internal housing and insulation to provide an outer protection of the internal components. This conventional configuration makes heat and energy recovery ventilators relatively expensive, and/or excessively labor intensive to manufacture. Unfortunately, the insulation alone does not always prevent condensation, and ultimately frost, from building up in the ventilator, particularly in extremely cold climates. Frost build-up in the ventilator is undesirable because it lowers the efficiency and/or ventilation rate of a heat exchanger within the ventilator and thus increases the operating costs of the ventilator.
In addition, many current heat and energy recovery ventilators require manual balancing of the incoming versus the outgoing air streams in order to achieve either a desired balanced or slightly imbalanced flow to the structure. When the flow of air streams are balanced, the incoming (i.e., supply) volumetric air flow (ft3/min) is equal to the outgoing (i.e., return or exhaust) volumetric air flow (ft3/min). Alternatively, the flow of air streams may be imbalanced such that the flow (ft3/min) of one air stream (e.g., supply) is greater than the flow (ft3/min) of the other air stream (e.g., return), thus causing a pressure differential between the interior and exterior of a structure. For example, a balanced, or slightly indoor positive (i.e., positive pressure inside the structure relative to outside the structure), pressure differential between the interior and exterior of a structure may be desired to prevent air and moisture from infiltrating into the structure from the outside to reduce the formation of mold and other undesirable conditions within the structure. The balanced pressure differential prevents sucking humidity from the outside into the wall cavities of the structure due to indoor negative pressure, or pushing humidity from inside the structure into the wall cavities due to a large positive indoor pressure differential.
As described above, conventional heat and energy ventilators require manual balancing of the these streams to attempt to maintain this pressure differential between inside and outside the structure. The conventional control systems have controlled either motor speed (constant RPM) or motor power draw (applied torque, e.g., constant torque) to control or balance the airstreams' velocities.
In general, current ventilators have not been configured to independently adjust the speed of the blowers and/or the rotational speed of the heat exchanger within the ventilator to maintain a desired environmental condition inside the structure in response to continuous measurements of environmental conditions such as humidity, temperature, and/or pressure. Accordingly, a need still exists for improved heat and energy recovery ventilators.